The top secret information was simply that it was still impossible to supply the Platform. Ships could be made faster than had ever been dreamed of before, but so long as any ship that went up could be destroyed on the way down, the supply of the Platform was impractical. But the ships were being built regardless, against the time when a way to get them down again was thought of. As of the moment it hadn't been thought of yet. But building the ships anyhow was unconscious genius, because nobody but Americans could imagine anything so foolish. The enemies of the Platform and of the United States knew that full-scale production of ships by some fantastic new method was in progress. The fact couldn't be hidden. But nobody in a country where material shortages were chronic could imagine building ships before a way to use them was known. So the Platform's enemies were convinced that the United States had something wholly new and very remarkable, and threatened their spies with unspeakable fates if they didn't find out what it was. They didn't find out. The rulers of the enemy nations knew, of course, that if a new--say--space-drive had been invented, they would very soon have to change their tune. So there were no more attacks on the Platform. It floated serenely overhead, sending down astronomical observations and solar-constant measurements and weather maps, while about it floated a screen of garbage and discarded tin cans. But Joe and Sally looked down where the ships were being built while the problem of how to use them was debated. "It's a tough nut to crack," said Joe dourly. It haunted him. Ships going up had to have crews. Crews had to come down again because they had to leave supplies at the Platform, not consume them there. Getting a ship up to orbit was easier than getting it down again. "The Navy's been working on light guided missiles," said Sally. "No good," snapped Joe. It wasn't. He'd been asked for advice. Could a space ship crew control guided missiles and fight its way back to ground with them? The answer was that it could. But guided missiles used to fight one's way down would have to be carried up first. And they would weigh as much as all the cargo a ship could carry. A ship that carried fighting rockets couldn't carry cargo. Cargo at the Platform was the thing desired. "All that's needed," said Sally, watching Joe's face, "is a slight touch of genius. There's been genius before now. Burning your cabin free with landing-rocket flames----" "Haney's idea," growled Joe dispiritedly. "And making more ships in a hurry with metal-concrete----" "Mike did that," said Joe ruefully. "But you made the garbage-screen for the Platform," insisted Sally. "Sanford had made a wisecrack," said Joe. "And it just happened that it made sense that he hadn't noticed." He grimaced. "You say something like that, now...."